The historic Richelieu River flows northwards over 115km, from Lake Champlain to Lake Saint Pierre on the Saint Lawrence River. There are two major obstacles to eel migration on this River : the Saint Ours Dam, 18 km upstream from the outlet, and the Chambly Dam , 70 km from the outlet. Downstream from the latter are the Chambly rapids and the remains of an old hydroelectric dam.
The Chambly dam is a concrete threshhold built in 1965. It replaces an old dam built out of wood and rocks that was part of the former hydroelectric project. The current dam has no generating station and its function is limited to maintaining the water level in the basin and canals upstream. At this point, the River is 270 meters wide and the threshold is approximately 5 meters high. The structure is completed by an energy dissipator that creates strong currents and white waters at the foot of the dam.
In 1997, MILIEU designed, manufactured and installed an eel ladder on the left side of the Chambly Dam. The installation of an eel ladder and a multispecies fishway in 2001 at Saint-Ours Dam completed the eel migration infrastructure on the Richelieu River. MILIEU has been operating and maintaining the Chambly eel ladder since its inception.